The invention relates to a system comprising a vacuum regulating valve and a control and regulating unit for pressure-regulated operation of a processing process under vacuum conditions.
In general, vacuum valves for regulating a volume or mass flow and for substantially gas-tight closure of a flow path, which leads through an opening formed in a valve housing are known in various embodiments from the prior art and are used in particular in vacuum chamber systems in the area of IC, semiconductor or substrate fabrication which must take place in a protected atmosphere as far as possible without the presence of contaminating particles. Such vacuum chamber systems comprise in particular at least one evacuatable vacuum chamber for receiving semiconductor elements or substrates to be processed or fabricated, which has at least one vacuum chamber opening, through which the semiconductor elements or other substrates can be guided into and out of the vacuum chamber as well as at least one vacuum pump for evacuating the vacuum chamber. For example, in a production plant for semiconductor wafers or liquid crystal substrates, highly sensitive semiconductor or liquid crystal elements run sequentially through a plurality of process vacuum chambers in which the parts located inside the process vacuum chambers are processed by means of a processing device in each case. Both during the processing process inside the process vacuum chambers and also during transport from chamber to chamber the highly sensitive semiconductor elements or substrates must always be located in a protected atmosphere—in particular in an air-free environment.
On the one hand, peripheral valves for opening and closing a gas supply or discharge and on the other hand, transfer valves for opening and closing the transfer openings of the vacuum chambers are used for this purpose for introducing and removing the parts.
The vacuum valves through which semiconductor parts pass are also designated as vacuum transfer valves as a result of the described area of application and the associated dimensioning, as rectangular valves as a result of their mostly rectangular opening cross-section and as slide valves, rectangular sliders or transfer slide valves as a result of their usual mode of operation.
Peripheral valves are used in particular for controlling or regulating the gas flow between a vacuum chamber and a vacuum pump or another vacuum chamber. Peripheral valves are located for example inside a pipe system between a process vacuum chamber or a transfer chamber and a vacuum pump, the atmosphere or another process vacuum chamber. The opening cross-section of such valves, also known as pump valves, is usually smaller than in the case of a vacuum transfer valve. Since peripheral valves are used, depending on the area of application, not only for complete opening and closing of an opening but also for controlling or regulating a flow through continuous adjustment of the opening cross-section between a complete open position and a gas-tight closed position, they are also designated as regulating valves. A possible peripheral valve for controlling or regulating the gas flow is the pendulum valve.
In a typical pendulum valve such as is known for example from U.S. Pat. No. 6,089,537 (Olmsted), in a first step a usually round valve disk is pivoted rotatably over an opening which is also usually round from a position which exposes the opening into an intermediate position which covers the opening. In the case of a slide valve such as is described in U.S. Pat. No. 6,416,037 (Geiser) or U.S. Pat. No. 6,056,266 (Blecha), the valve disk and also the opening is usually configured to be rectangular and in this first step is pushed linearly from a position which exposes the opening into an intermediate position which covers the opening. In this intermediate position, the valve disk of the pendulum valve or slide valve is located in a spaced-apart opposite position to the valve seat surrounding the opening. In a second step, the distance between the valve disk and the valve seat is reduced so that the valve disk and the valve seat are pressed uniformly onto one another and the opening is closed in a substantially gastight manner. This second movement preferably takes place substantially in a perpendicular position to the valve seat. The sealing can be accomplished, for example, either via a sealing ring arranged on the closure side of the valve disk which is pressed onto the valve seating which runs around the opening or via a sealing ring on the valve seat against which the closure side of the valve disk is pressed. As a result of the closure process which takes place in two steps, the sealing ring is barely subjected to shear forces which would destroy the sealing ring between the valve disk and the valve seat since the movement of the valve disk in the second step takes place substantially rectilinearly perpendicularly onto the valve seat.
Different sealing processes are known from the prior art, for example, from U.S. Pat. No. 6,629,682 B2 (Duelli). A suitable material for sealing rings and seals in vacuum valves is, for example, fluororubber, also known as FKM, in particular the fluoroelastomer known under the trade name “Viton” as well as perfluororubber, FFKM for short.
Various drive systems for achieving this combination of a rotational movement of the valve disk in the case of a pendulum valve and translational movement of the valve disk in the case of the slide valve parallel over the opening and a substantially translational movement perpendicular to the opening are known, for example, from U.S. Pat. No. 6,089,537 (Olmstead) for a pendulum valve and from U.S. Pat. No. 6,416,037 (Geiser) for a slide valve.
The pressing of the valve disk onto the valve seat must be accomplished in such a manner that both the required gas-tightness is ensured within the entire pressure range and also any damage to the sealing medium, in particular the sealing ring in the form of an O ring, due to excessive pressure loading is avoided. In order to avoid this, known valves provide a contact pressure regulation of the valve disk regulated depending on the pressure difference prevailing between the two valve disk sides.
Particularly in the case of large pressure fluctuations or when changing from negative pressure to positive pressure or conversely, however a uniform force distribution along the entire circumference of the sealing ring cannot always be ensured. In general, it is strived to decouple the sealing ring from supporting forces which arise from the pressure applied to the valve. In U.S. Pat. No. 6,629,682 (Duelli), for this purpose, for example a vacuum valve with a sealing medium is proposed which is composed of a sealing ring and an adjacently located support ring, so that the sealing ring is substantially freed from support forces.
In order to achieve the required gas tightness, optionally both for positive and also negative pressure, in addition to or alternatively to the second movement step some known pendulum valves or slide valves provide a valve ring surrounding the opening which is displaceable perpendicular to the valve disk which is pressed onto the valve disk for gas-tight closing of the valve. Such valves with valve rings which are actively displaceable relative to the valve disk are known, for example from DE 1 264 191 B1, DE 34 47 008 C2, U.S. Pat. No. 3,145,969 (von Zweck) and DE 77 31 993 U. U.S. Pat. No. 5,577,707 (Brida) describes a pendulum valve with a valve casing having an opening and a valve disk which is pivotable parallel over the opening for controlling a flow through the opening. A valve ring which encloses the opening is actively movable perpendicularly in the direction of the valve disk by means of a plurality of springs and compressed air cylinders. A possible further development of this pendulum valve is proposed in US 2005/0067603 A1 (Lucas et al.).
Since aforesaid valves are used inter alia in the fabrication of highly sensitive semiconductor elements, the particle generation caused in particular by actuation of the valve and by the mechanical loading of the valve closure member and the number of free particles in the valve chamber should be kept as small as possible. The particle generation is primarily a consequence of friction, for example due to metal-metal contact and due to abrasion.
As described above, vacuum regulating valves are used for adjusting a defined process environment in a process chamber. The regulation is typically accomplished here by means of a pressure signal which provides information relating to the chamber internal pressure and by means of a target value, i.e. a desired pressure which should be achieved by means of the regulation. The position of a valve closure (valve disk) is then varied in the course of the regulation so that the desired pressure is achieved within a certain time interval.
Alternatively to the regulation, vacuum regulating valves can also be operated in a controlled manner by means of known process parameters such as, for example a desired pressure to be achieved in the process chamber in a predefined time. For this purpose, for example relevant desired positions for the valve disk are provided and this position is approached in likewise predefined times.
Both the above methods have their specific advantages and disadvantages. Thus, a desired pressure in the process chamber can be set in a relatively short time by means of a predefined control but as a result of a typically lacking feedback (e.g. current pressure information), a prediction on the currently prevailing pressure can only be made with reservations. Any undesired influences on the production process such as, for example a changed gas inlet or a leak of the process chamber remain completely unidentified and then typically result in a reduction in the fabrication quality.
In contrast to control, a regulation of the pressure in a process chamber is more time-intensive. A feedback signal—typically produced by a pressure sensor which measures the actually applied chamber pressure—is recorded and processed with a natural delay. A regulation based thereon is consequently made with a corresponding delay and results in a correspondingly later setting of the desired pressure. On the other hand, the regulation of the desired pressure may reliably set this even with varying gas inlets or pressure fluctuations in the process chamber. As a result of the more reliable process safety in view of the definitive chamber internal pressure, in most cases a regulation of the valve is preferably used.
It is therefore the object of the invention to provide an improved vacuum valve with a regulation which is able to avoid the aforesaid disadvantages.
In particular, it is the object of the invention to provide an improved vacuum valve with a regulation which exhibits an improved, i.e. more rapid and more reliable regulating behaviour.
These objects are solved by implementing the characterizing features of the independent claims. Features which further develop the invention in alternative or advantageous manner can be deduced from the dependent patent claims.